1. Field of the Invention
This invention relates to an electromagnetic clutch, and more particularly to an electromagnetic clutch for transmitting driving force from a drive source to a drive shaft of a refrigerant compressor.
2. Description of the Prior Art
FIG. 1 is a perspective view, partly in section, of a conventional electromagnetic clutch.
The electromagnetic clutch 300 includes a hub 310 having a flange portion 311 and rigidly fitted on a drive shaft 302 of a refrigerant compressor, a rotor 320 driven by torque from an engine (not shown) for rotation about the drive shaft 302, an armature plate 330 which is magnetically attracted into abutment with the rotor 320 when a magnetic coil 321 arranged in the rotor 320 is energized, and three leaf springs 340 interposed between the flange portion 311 of the hub 310 and the armature plate 330 for returning the armature plate 330 to its off position when the magnetic coil 321 is deenergized. The armature plate 330 is comprised of an outer disk 330a and an inner disk 330b joined to an inner periphery of the outer disk 330a via a jointing metal 330c.
The rotor 320 has a pulley groove 360 circumferentially formed in its outer peripheral surface, and a V-belt, not shown, extends around the pulley groove 360, for connecting the rotor 320 to a crankshaft of the engine, not shown.
Rubber stoppers 350a, 350b and 350c are provided respectively between the leaf springs 340 and the inner disk 330b of the armature plate 330 such that they have preloads which prevent rattle.
When the magnetic coil 321 is not energized, the leaf springs 340 having resilient properties hold the armature plate 330 in its off position at a predetermined distance from a friction surface of the rotor 320, whereby driving force of the engine is inhibited from being transmitted to the refrigerant compressor, and hence the rotor 320 rotates in a disconnected state or idles.
On the other hand, when the magnetic coil 321 is energized for generation of electromagnetic force, the armature plate 330 is magnetically attracted into abutment with the friction surface of the rotor 320 against the pulling or returning force of the leaf springs 340, whereby the driving force from the engine is transmitted to the drive shaft 302 of the refrigerant compressor.
According to the above conventional electromagnetic clutch, since the armature plate 330 and the leaf springs 340 are united by rivets 316, 317, a variation in torque generated within the refrigerant compressor (i.e. a variation in reaction force exerted against torque from the engine, which is dependent on load on the compressor and the like) is accommodated by elastic deformation or deflection of the leaf springs 340 having resilient properties. However, when the leaf springs 340 alone are used for the purpose of accommodating the variation in the torque from the refrigerant compressor, the variation in the torque (reaction force) cannot be fully accommodated, depending on rotational speed of the compressor, which can result in a large variation in the torque from the refrigerant compressor.